The present invention relates to hydrophilic polyolefins. More particularly, the present invention relates to hydrophilic shaped polyolefin structures having surfaces modified by the presence of groups which render such surfaces hydrophilic.
As used herein, the term "shaped polyolefin structure" is used broadly to include any solid form of a polyolefin, in contrast to a polyolefin in a gaseous or liquid phase, or in solution. Thus, the polyolefin can be in particulate form, such as a powder or granules or chips, a molded article, an extruded shape, fibers, woven or nonwoven fabrics, films, or the like. For convenience, the discussion which follows will be limited to fibers and nonwoven fabrics or webs. Such discussion, however, is not to be construed as in any way limiting either the spirit or the scope of the present invention.
Polyolefin fibers presently are employed in a variety of commercial applications. For some applications, however, such as in disposable nonwoven absorbent products, the hydrophobic nature of polyolefin is a disadvantage. Even in earlier nonfiber products, there was a need for a hydrophilic polyolefin. Consequently, efforts were directed to methods of altering the hydrophobic nature of polyolefin surfaces.
One of the earliest of such methods is described in British Patent Specification No. 952,111. The patent describes a method of obtaining durable, lasting, chemically active polyolefin surfaces to which adhesives, dyes, inks, and coatings will adhere, and which surfaces also have acquired antistatic properties. In other words, the described method purportedly renders the polyolefin surfaces hydrophilic. The method involves exposing the surface of a solid polyolefin to a mixture of gaseous sulfur dioxide and chlorine in the presence of ultraviolet light to form chlorosulfo (--SO.sub.2 Cl) groups on such surface, allegedly leaving the bulk of the polymer unchanged. The chlorosulfo groups then are reacted with a reagent selected from the class consisting of ammonia, monoamines, polyamines, monohydric alcohols, polyhydric alcohols, alkylene oxides, and aqueous alkali metal hydroxides.
U.S. Pat. No. 3,624,054 describes the chlorosulfonation reaction of the above reference without a subsequent treatment with an amine, an epoxide, or a hydroxy-containing compound. According to the disclosure, powdered polyethylene is mixed with glass beads and treated with a gaseous mixture of sulfur dioxide and chlorine in the presence of actinic, e.g., ultraviolet, light. Care is taken to exclude all oxygen and water from the reaction vessel. The treated polyethylene is used to make nonconductive insulating coatings for electrical wiring.
U.S. Pat. Nos. 3,765,948 and 4,000,967 relate to wettable nonwoven structures such as a battery separator. Briefly, a nonwoven mat of polyolefin fiber is contacted with a gaseous mixture of sulfur dioxide and chlorine in the presence of ultraviolet radiation, followed by treatment with an amine.
These prior art chlorosulfonation reactions all are equivalent, if not identical, and introduces chlorosulfo groups on the surface of the polymer. In all but one reference, the chlorosulfo groups then are reacted with amine to give amidosulfo groups. While chlorosulfonation of the polyolefin surface undoubtedly occurs, it does not appear to occur extensively. Furthermore, the amidosulfo group, especially at relatively low concentrations, is not particularly effective in altering the hydrophobic nature of the polyolefin surface.
In addition to chlorosulfonation, such prior art procedures are believed to result in extensive chlorination. In fact, chlorination appears to be the predominant reaction. Moreover, these prior art reactions are not limited to surfaces but affect the bulk of the article being treated. Consequently, the extensive chlorination which apparently takes place can have a significant adverse effect on the physical properties of the polyolefin article, especially when fibers or nonwoven fabrics or webs are being treated.
Consequently, there is a need for a method of effectively rendering polyolefins hydrophilic which lacks or minimizes competing side reactions. There also is a need for a method of rendering the surfaces of polyolefin structures hydrophilic.